Persistent herpes simplex virus (HSV) infections were established in human Burkitt lymphoma cells that required no external supportive measures. Cells were positive for HSV antigens and contained up to 8 percent HSV DNA. Differences in cell response and virus strains were observed. A Moloney murine sarcoma virus (MSV) specific p60 with murine group p30, and p15E antigenic determinants is detected in all cells transformed by the m-l MSV genome. P30 is only detected in virions and not in cells, while p60 is stable and uncleaved in cells.